I'm already using radeon FOSS driver (instead of fglrx)

==========old:
from:
http://askubuntu.com/questions/324733/how-to-enable-the-radeon-dynamic-power-management-feature

cat /sys/kernel/debug/dri/64/radeon_pm_info
You should see something like this:

uvd    vclk: 0 dclk: 0
power level 0    sclk: 22000 mclk: 25000 vddc: 900

You can further configure DPM by opening /etc/rc.local and adding the following line:

echo parameter > /sys/class/drm/card0/device/power_dpm_state

Where "parameter" can be:

    battery (a set of performance levels targeted for optimal operation on battery)
    balanced (a set of performance levels targeted for optimal every day use)
    performance (a set of performance levels targeted for the highest GPU performance)
=============
http://linrunner.de/en/tlp/docs/tlp-configuration.html
change some radeon settings in tlp !
